The present invention generally concerns a system for characterizing the handling performance of tires, and more particularly, concerns a test procedure used to evaluate various parameters related to handling characteristics of self-supporting tires. The subject test procedure is preferably utilized in conjunction with a common reporting grid and rating scale to yield a standardized system for evaluating tire performance.
The ability to effectively operate a vehicle after experiencing loss of tire pressure offers many practical advantages. The benefits that such a driving ability can provide has led to consumer demand for and commercial development of xe2x80x9cself-supportingxe2x80x9d or xe2x80x9crun-flatxe2x80x9d tires. Such tires typically incorporate additional supportive features to provide a vehicle with extended mobility upon the event that a tire loses air pressure. Examples of the type of supportive features characteristic of a self-supporting tire may include special bead designs, sidewall reinforcements, summit adjustments, internal tire safety supports, etc.
Several specific self-supporting tire designs are currently available in the marketplace, including the ZP (Zero Pressure) brand tire and the PAX brand tire system of Michelin North America, Inc. Selected aspects of such extended mobility products are disclosed in U.S. Pat. Nos. 5,868,190 (Willard Jr. et al.), 5,891,279 (Lacour), and 5,749,984 (Frey et al.). Each of the foregoing patents is hereby fully incorporated into this application for all purposes by present reference thereto.
Future development of self-supporting tires and related products requires effective evaluation of their performance characteristics. A self-supporting tire preferably achieves desired levels of performance when the tire is both inflated and deflated. Since a major objective of self-supporting tires is to provide mobility upon a tire losing pressure, notable evaluation criteria often relate to deflated mobility performance.
In general, it is preferred to develop self-supporting tires that can achieve certain fundamental objectives, including operation at a level comparable to that of a conventional inflated tire. Examples of other performance objectives include enhanced low-pressure handling capabilities and bead retention, and acceptable handling and sufficient durability at zero pressure situations. In whole, the goal for designing a self-supporting tire is to enable a motorist to continue driving for some distance in a relatively effective manner and appropriate fashion even after a loss of tire pressure.
In order to determine when a self-supporting tire achieves its preferred performance objectives, comprehensive tests are desired so as to provide standardized evaluation of tire performance. It may thus be desirable to develop a deflated handling test that would provide a reliable measure of tire performance when a tirexe2x80x94vehicle combination is subjected to a plurality of predetermined driving maneuvers. Such a deflated handling test is preferably formulated in such a particular way that the test results provide a standardized system for evaluating tire handling characteristics. A testing system may preferably be designed such that dispersion of test results among different testers at different times or on different test vehicles is minimized.
An example of methodology relating to the measurement of tire handling characteristics is disclosed in U.S. Pat. No. 4,969,212 (Walter), which by reference is hereby incorporated into the present application for all purposes. While various systems and procedures have been developed that relate to self-supporting tire technology and to general tire testing methodology, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.
In view of the recognized features encountered in the prior art and addressed by the present subject matter, an improved testing system for characterizing deflated tire handling performance has been developed. Aspects of the varied embodiments of the subject testing system include a standardized testing procedure, a uniform reporting grid, and a common rating scale. Exemplary testing procedures preferably involve subjecting a test vehicle with selected deflated tires to a multitude of driving maneuvers. Both subjective perceptions and objective measurements are then preferably obtained in accordance with predetermined characteristics exhibited by the tested tire during the driving maneuvers. A common philosophy and approach is preferably established for the driving maneuvers and performance perceptions such that uniform results are more easily obtained. The performance perception ratings are then preferably inputted to an algorithm that provides an overall subjective rating of a tire""s deflated handling performance.
Various features and aspects of the subject testing system and related procedure offer a plurality of advantages. Establishing a common and particular testing system and method preferably enables the dispersion level of the new method to improve upon existing test method dispersion levels. The subject system also preferably provides a testing procedure such that the minimum threshold level of tire acceptability is the same for a variety of worldwide testing facilities, personnel, and products. The disclosed testing methodology is also preferably formulated such that communication about the testing system among internal and external entities in the marketplace is readily facilitated.
Yet another advantage of aspects of the presently disclosed technology is that the subject method involves subjecting a tirexe2x80x94test vehicle combination to a variety of different maneuvers such that numerous potential driving conditions are simulated. Exemplary embodiments of the subject deflated handling test procedures may incorporate selected maneuvers including steady state, throttle lift off, transient state, and emergency maneuvers.
Although a standardized testing procedure utilized by numerous testing groups may offer more uniform results and a common rating scale, the testing methodology and related features disclosed herein provide many testing options. Not only can different driving maneuvers be incorporated into a testing process, but so can the various subjective and objective criteria that are rated in accordance with a handling performance test.
In one exemplary embodiment of the present subject matter, a method for rating the handling performance of tires involves positioning selected tires on a test vehicle and subjecting the tirexe2x80x94test vehicle combination to certain predetermined maneuvers. Performance ratings are then preferably obtained in accordance with the predefined maneuvers.
More preferably, such a method for rating handling performance includes several steps, including obtaining a g-value corresponding to the lateral acceleration of the test vehicle during a selected predetermined maneuver and at a point when the tire exhibits an established level of stability. In accordance with the subject exemplary embodiment, steady state and transient ratings are also assigned when the tirexe2x80x94test vehicle combination is subjected to steady state and transient maneuvers, respectively. The assigned steady state and transient ratings and the obtained g-value are then used to calculate an initial tire performance rating.
Another exemplary embodiment of the present technology concerns a rating process for subjectively evaluating the deflated handling performance of tires. Such a rating process may incorporate the assignment of various ratings corresponding to the handling performance of a deflated tire when subjected to predetermined maneuvers. The maneuvers and corresponding ratings preferably represent at least one of each steady state, transient, and emergency driving situations. A deflated tire performance rating is then preferably obtained via algorithmic formulas wherein the steady state, transient, and emergency ratings are provided as input to the algorithm. In other related exemplary embodiments, a throttle lift off maneuver and corresponding rating may also be obtained and incorporated into the overall deflated tire performance rating.
Yet another exemplary embodiment of the subject methodology relates to a subjective test method used to provide a performance rating for self-supporting tires. In accordance with this particular embodiment, a self-supporting tire is positioned on a test vehicle, which is then subjected to a plurality of testing maneuvers. When the tire-vehicle combination is subjected to a steady state testing maneuver, a value for the lateral acceleration of the test vehicle is preferably obtained when the tire achieves a predetermined level of stability. At least one steady state grade is also assigned to selected performance variables when the tirexe2x80x94test vehicle combination is subjected to a steady state maneuver. The tirexe2x80x94test vehicle combination is also preferably subjected to at least one throttle lift-off maneuver, at least one transient maneuver, and at least one emergency maneuver, at which point respective values are assigned to performance variables for each maneuver. All performance values, including lateral acceleration, steady state performance variable(s), transient performance variable(s), throttle lift-off performance variable(s), and emergency performance variable(s) are then preferably utilized to calculate a tire performance rating.
A still further exemplary embodiment of the disclosed testing technology corresponds to a comprehensive system for evaluating tire handling performance, comprising a testing process, a reporting grid, and an algorithm. A tire is preferably subjected to a plurality of predetermined maneuvers in accordance with the testing process such that performance ratings representative of aspects of tire handling performance are determined. The performance ratings and other data may then be recorded in the standardized reporting grid, and a predetermined combination of that information is then preferably used to calculate an overall tire performance rating.
An additional embodiment of aspects of the present subject matter concerns a standardized algorithm for obtaining a deflated performance rating for self-supporting tires. A self-supporting tire is positioned on a test vehicle and the resultant combination then endures a plurality of maneuvers, and various test ratings are obtained in accordance with deflated handling performance during such maneuvers. The standardized algorithm also preferably includes the steps of obtaining a g-value for the lateral acceleration of the test vehicle when the tire-vehicle system achieves a predetermined level of instability upon subjection to a steady state driving maneuver and assigning a plurality of performance values for predefined testing criteria based on deflated tire performance when subjected to certain maneuvers. An initial tire rating may then be calculated based on the g-value and the assigned plurality of performance values. Emergency performance values may also preferably be obtained in accordance with this exemplary algorithm and selected of these emergency performance values in combination with the initial tire rating may then be used to calculate an overall tire rating.
Additional objects and advantages of the present subject matter are set forth in, or will be apparent to, those of ordinary skill in the art from the detailed description herein. Also, it should be further appreciated that modifications and variations to the specifically illustrated, referred and discussed features and steps hereof may be practiced in various embodiments and uses of the invention without departing from the spirit and scope of the subject matter. Variations may include, but are not limited to, substitution of equivalent means, features, or steps for those illustrated, referenced, or discussed, and the functional, operational, or positional reversal of various parts, features, steps, or the like.
Still further, it is to be understood that different embodiments, as well as different presently preferred embodiments, of this invention may include various combinations or configurations of presently disclosed features, steps, or elements, or their equivalents (including combinations of features, parts, or steps or configurations thereof not expressly shown in the figures or stated in the detailed description of such figures). Additional embodiments of the present subject matter, not necessarily expressed in this summarized section, may include and incorporate various combinations of aspects of features, components, or steps referenced in the summarized objectives above, and/or other features, components, or steps as otherwise discussed in this application. Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the remainder of the specification.